1. Field of the Invention
The present invention relates to a liquid jetting apparatus including a cavity unit having a plurality of nozzles through each of which a liquid is jetted and pressure chambers communicating with the nozzles respectively, and an actuator unit applying jetting pressures to the pressure chambers.
2. Description of the Related Art
As a conventional liquid jetting apparatus, there is, for example, an ink-jet head which includes: a plate-shaped cavity unit having one surface in which a plurality of nozzles for jetting minute ink droplets are formed and other surface on which a plurality of pressure chambers communicating with the nozzles respectively are opened; and a plate-shaped actuator unit which is stacked on the cavity unit to apply jetting pressures to the pressure chambers of the cavity unit.
The actuator unit has a plurality of stacked ceramics layers, and individual electrodes which are individually disposed so as to correspond to the pressure chambers of the cavity unit respectively and a common electrode common to all the pressure chambers (ground electrode) are disposed between the ceramics layers. A predetermined number of sets of the individual electrodes and the common electrode are arranged alternately. In each of the ceramics layers, portions sandwiched by the individual electrodes and the common electrode are active portions. The actuator unit is joined to the aforesaid other surface of the cavity unit so that the active portions face the pressure chambers respectively. When voltage is applied between the individual electrode and the common electrode of the actuator unit to drive the active portion, the actuator unit deforms to change the volume of the pressure chamber of the cavity unit. Consequently, a jetting pressure is applied to the liquid (ink) in the pressure chamber, so that the ink is jetted from the nozzle corresponding to this pressure chamber.
Since the actuator unit has a ceramics sintered compact, the actuator unit easily suffers a minute crack due to the deformation when fired or driven. When such a defect exists, there is a risk of the ink in the pressure chambers entering a crack at a place where the ceramics layer of the actuator unit is in direct contact with a cavity plate. In such a case, the ink entering the crack penetrates into the ceramics layer, which in turn is likely to cause electric short-circuit between the individual electrodes and the common electrode.
To avoid this problem, in an ink-jet head described in Japanese Patent Application Laid-open No. 2006-341509 (pages 5 to 7, FIG. 3), a conductive protection film is formed on a joint surface, of an actuator unit, joined to a cavity unit, thereby preventing a ceramics layer from coming into direct contact with ink in pressure chambers. This protection film is made of conductive paste which is fired after applied on the actuator unit. The protection film further prevents the ink in the pressure chambers from being charged.